Deep high capacity capacitor for bulk substrates

ABSTRACT

A deep trench capacitor having a high capacity is formed into a deep trench having faceted sidewall surfaces. The deep trench is located in a bulk silicon substrate that contains an upper region of undoped silicon and a lower region of n-doped silicon. The lower region of the bulk silicon substrate includes alternating regions of n-doped silicon that have a first boron concentration (i.e., boron deficient regions), and regions of n-doped silicon that have a second boron concentration which is greater than the first boron concentration (i.e., boron rich regions).

BACKGROUND

The present application relates to a semiconductor structure and amethod of forming the same. More particularly, the present applicationrelates to a semiconductor structure including a deep trench capacitorhaving a high capacity and located in a bulk silicon substrate as wellas a method of forming the same.

In the semiconductor industry, deep trenches, which typical have a depthexceeding 1 micron (μm), are employed to provide a variety of usefuldevices including a deep trench capacitor. The deep trenches may beutilized in a stand-alone semiconductor circuit such as, for example, adynamic random access memory (DRAM) circuit to provide deep trenchcapacitors, or the deep trenches may be utilized as an embedded circuitcomponent of a semiconductor chip that also includes other semiconductorcircuits such as a processor core or other logic circuits. Particularly,embedded deep trench capacitors may be used to enable an embedded memorydevice, for example, an embedded dynamic random access memory (eDRAM)cell, a passive component of a radio frequency (RF) circuit, or adecoupling capacitor that provides a stable voltage supply in asemiconductor circuit.

Typically, deep trench capacitors are formed into a semiconductor handlesubstrate of a semiconductor-on-insulator (SOI) substrates; thesemiconductor handle substrate is located beneath a buried insulatorlayer and an active semiconductor device layer of the SOI substrate. SOIsubstrates have been employed in the semiconductor industry forperformance benefits do to reduced capacitive coupling betweensemiconductor devices and the semiconductor handle substrate.

Despite the benefits that SOI substrates provide in eDRAM manufacturing,there is an ongoing desire to replace SOI substrates with bulksemiconductor substrates since bulk semiconductor substrates are cheaperand are more readily available. Notably, there is a need for providing adeep trench capacitor that has a high capacity and that is formed in abulk semiconductor substrate.

SUMMARY

A deep trench capacitor having a high capacity is formed into a deeptrench having faceted sidewall surfaces. The deep trench is located in abulk silicon substrate that contains an upper region of undoped siliconand a lower region of n-doped silicon. The lower region of the bulksilicon substrate includes alternating regions of n-doped silicon thathave a first boron concentration (i.e., boron deficient regions), andregions of n-doped silicon that have a second boron concentration whichis greater than the first boron concentration (i.e., boron rich regionsas compared to the boron deficient regions).

In aspect of the present application, a semiconductor structure isprovided. In one embodiment, the semiconductor structure includes a deeptrench capacitor present in a deep trench having faceted sidewallsurfaces that is located in a bulk silicon substrate, wherein the bulksilicon substrate includes an upper region of undoped silicon and alower region of n-doped silicon, wherein the lower region comprisesalternating regions of n-doped silicon that have a first boronconcentration, and regions of n-doped silicon that have a second boronconcentration which is greater than the first boron concentration.

In another embodiment, the semiconductor structure includes a first deeptrench capacitor present in a first deep trench having faceted sidewallsurfaces that is located in a bulk silicon substrate, wherein the bulksilicon substrate includes an upper region of undoped silicon and alower region of n-doped silicon, wherein the lower region comprisesalternating regions of n-doped silicon that have a first boronconcentration, and regions of n-doped silicon that have a second boronconcentration which is greater than the first boron concentration. Asecond deep trench capacitor is present in a second deep trench havingfaceted sidewall surfaces that is located in the bulk silicon substrate,wherein a flowable dielectric material is located in a lower portion ofthe second deep trench and located entirely beneath the second deeptrench capacitor.

In another aspect of the present application, a method of forming asemiconductor structure is provided. In one embodiment, the method mayinclude first forming a deep trench in a precursor bulk semiconductorsubstrate, wherein the precursor bulk semiconductor substrate comprises,from bottom to top, a base silicon substrate, a semiconductor materialstack of alternating layers of boron doped silicon and silicon, and asilicon device layer, and wherein the deep trench exposes a sub-surfaceof the base silicon substrate. Next, a hanging spacer is formed onphysically exposed sidewall surfaces of the silicon device layer withinthe deep trench. A crystallographic etch is then performed in the deeptrench that etches the layers of silicon selective to layers of borondoped silicon, wherein the etched silicon surfaces in the deep trenchhave a faceted sidewall surface. Next, the deep trench containingfaceted sidewall surfaces is filled with an n-doped source material. Ananneal is then performed to drive n-type dopant from the n-doped sourcematerial into the base silicon substrate, the semiconductor materialstack, and the silicon device layer of the precursor bulk semiconductorsubstrate. Next, the n-doped source material and each hanging spacer areremoved from the deep trench containing the faceted sidewall surfaces,and thereafter, a deep trench capacitor is formed in the deep trenchcontaining the faceted sidewall surfaces.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional view of an exemplary semiconductor structureincluding, from bottom to top, a base silicon substrate, a semiconductormaterial stack of alternating layers of boron doped silicon and silicon,and a silicon device layer that can be employed in the presentapplication.

FIG. 2 is a cross sectional view of the exemplary semiconductorstructure of FIG. 1 after forming a deep trench that exposes asub-surface of the base silicon substrate.

FIG. 3 is a cross sectional view of the exemplary semiconductorstructure of FIG. 2 after forming a hanging spacer on physically exposedsidewall surfaces of the silicon device layer within the deep trench.

FIG. 4A is a cross sectional view of the exemplary semiconductorstructure of FIG. 3 after performing a crystallographic etch in the deeptrench that etches the layers of silicon selective to layers of borondoped silicon, wherein the etched silicon surfaces in the deep trenchhave a faceted sidewall surface.

FIG. 4B is a cross sectional view of an exemplary semiconductorstructure such as shown in FIG. 4A with less layers within thesemiconductor material stack.

FIG. 5 is a cross sectional view of the exemplary semiconductorstructure of FIG. 4B after filling the deep trench with an n-dopedsource material.

FIG. 6 is a cross sectional view of the exemplary semiconductorstructure of FIG. 5 after performing an anneal to drive n-type dopantfrom the n-doped source material into the base silicon substrate, thesemiconductor material stack, and the silicon device layer.

FIG. 7 is a cross sectional view of the exemplary semiconductorstructure of FIG. 6 after removing the n-doped source material and eachhanging spacer from the deep trench.

FIG. 8 is a cross sectional view of the exemplary semiconductorstructure of FIG. 7 after forming a first conductive layer.

FIG. 9 is a cross sectional view of the exemplary semiconductorstructure of FIG. 8 after forming a dielectric material layer.

FIG. 10 is a cross sectional view of the exemplary semiconductorstructure of FIG. 9 after forming a second conductive layer.

FIG. 11 is a cross sectional view of the exemplary semiconductorstructure of FIG. 10 after removing portions of the first conductivelayer, the dielectric material layer and the second conductive layerthat are present outside the deep trench, while maintaining portions ofthe first conductive layer, the dielectric material layer and the secondconductive layer that are present inside the deep trench.

FIG. 12 is a cross sectional view of the exemplary semiconductorstructure of FIG. 11 after forming at least one deep trench contact.

FIG. 13 is a cross sectional view illustrating another exemplarysemiconductor structure in accordance with the present application.

DETAILED DESCRIPTION

The present application will now be described in greater detail byreferring to the following discussion and drawings that accompany thepresent application. It is noted that the drawings of the presentapplication are provided for illustrative purposes only and, as such,the drawings are not drawn to scale. It is also noted that like andcorresponding elements are referred to by like reference numerals.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide an understanding ofthe various embodiments of the present application. However, it will beappreciated by one of ordinary skill in the art that the variousembodiments of the present application may be practiced without thesespecific details. In other instances, well-known structures orprocessing steps have not been described in detail in order to avoidobscuring the present application.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “beneath” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

Referring first to FIG. 1, there is illustrated an exemplarysemiconductor structure that can be employed in the present application.Notably, the exemplary semiconductor structure shown in FIG. 1 includes,from bottom to top, a base silicon substrate 10, a semiconductormaterial stack MS1, and a silicon device layer 16. No insulator layer islocated between any of the base silicon substrate 10, the semiconductormaterial stack MS1, and the silicon device layer 16, and no insulatorlayer is present in the semiconductor material stack MS1. Thus, the basesilicon substrate 10, the semiconductor material stack MS1, and thesilicon device layer 16 collectively may be referred to as a precursorbulk semiconductor substrate.

The base silicon substrate 10 is typically a single crystalline siliconlayer. The base silicon substrate 10 is typically non-doped at thispoint of the present application. The base silicon substrate 10 may haveany well known crystallographic orientation including, for example,{100}, {110}, or {111}. The base silicon substrate 10 can have athickness from 500 microns to 1000 microns. Other thicknesses that arelesser than, or greater than, the aforementioned thickness values mayalso be used as the thickness of the base silicon substrate 10.

The semiconductor material stack MS1 includes alternating layers ofboron doped silicon or B:Si, for short, (e.g., 12A, 12B, 12C, 12E), andsilicon (e.g., 14A, 14B, 14C, 14D). In accordance with the presentapplication, each layer of silicon of the semiconductor material stackMS1 is sandwiched between a lower boron doped silicon layer and an upperboron doped silicon layer. Thus, the semiconductor material stack MS1includes ‘n’ number of silicon layers, wherein n is at least 1, and n+1number of boron doped silicon layers; the upper value of ‘n’ may varyand is used to determine the overall thickness of the precursor bulksemiconductor substrate. By way of one example, five layers of borondoped silicon, and four layers of silicon are illustrated within thesemiconductor material stack MS1 of FIG. 1. Each of the various layerswithin the semiconductor material stack MS1 is typically singlecrystalline.

The term “boron doped silicon” is used throughout the presentapplication to denote a silicon layer that is doped with boron. Theconcentration of boron that is present in the boron doped silicon layers(e.g., 12A, 12B, 12C, 12E) of the semiconductor material stack MS1 canbe from 1E18 atoms/cm³ to 10E18 atoms/cm³. Each silicon layer (e.g.,14A, 14B, 14C, 14D) of the semiconductor material stack MS1 is notalloyed with another semiconductor material and is non-doped at thispoint of the present application.

Each boron doped silicon layer (e.g., 12A, 12B, 12C, 12E) of thesemiconductor material stack MS1 has a first thickness, while eachsilicon layer (e.g., 14A, 14B, 14C, 14D) of the semiconductor materialstack MS1 has a second thickness that is greater than the firstthickness. In one example, each boron doped silicon layer (e.g., 12A,12B, 12C, 12E) of the semiconductor material stack MS1 may have athickness from 2 nm to 10 nm, while each silicon layer (e.g., 14A, 14B,14C, 14D) of the semiconductor material stack MS1 may have a thicknessfrom 50 nm to 500 nm.

The semiconductor material stack MS1 can be formed utilizing anepitaxial growth or epitaxial deposition process. The terms “epitaxialgrowth and/or deposition” and “epitaxially formed and/or grown” mean thegrowth of a semiconductor material on a deposition surface of asemiconductor material, in which the semiconductor material being grownhas the same crystalline characteristics as the semiconductor materialof the deposition surface. In an epitaxial deposition process, thechemical reactants provided by the source gases are controlled and thesystem parameters are set so that the depositing atoms arrive at thedeposition surface of a semiconductor material with sufficient energy tomove around on the surface and orient themselves to the crystalarrangement of the atoms of the deposition surface. Therefore, anepitaxial semiconductor material that is formed by an epitaxialdeposition process has the same crystalline characteristics as thedeposition surface on which it is formed. For example, an epitaxialsemiconductor material deposited on a {100} crystal surface will take ona {100} orientation. Thus, each layer within the semiconductor materialstack MS1 has an epitaxial relationship with each other as well ashaving an epitaxial relationship with the growth surface of the basesilicon substrate 10.

Examples of various epitaxial growth processes that are suitable for usein forming the semiconductor material stack MS1 include, e.g., rapidthermal chemical vapor deposition (RTCVD), low-energy plasma deposition(LEPD), ultra-high vacuum chemical vapor deposition (UHVCVD),atmospheric pressure chemical vapor deposition (APCVD), molecular beamepitaxy (MBE) or metal-organic CVD (MOCVD). The temperature forepitaxial deposition typically ranges from 250° C. to 900° C. Althoughhigher temperature typically results in faster deposition, the fasterdeposition may result in crystal defects and film cracking. A number ofwell known silicon source gases such as, for example, a silane, may beused for the deposition of the various layers of the semiconductormaterial stack MS1. Carrier gases like hydrogen, nitrogen, helium andargon can be used. In the present application, each boron doped siliconlayer within the semiconductor material stack MS1 is formed byintroducing a boron dopant into the silicon source gas, and each siliconlayer of the semiconductor material stack MS1 is formed by eliminatingthe boron dopant from the silicon source gas.

The silicon device layer 16 is formed upon the topmost boron dopedsilicon layer (e.g., 12E) of the semiconductor material stack MS1utilizing an epitaxial growth process as mentioned above without thepresence of any boron dopant within the silicon source gas. The silicondevice layer 16 is typically a single crystalline silicon layer. Thesilicon device layer 16 is typically non-doped at this point of thepresent application. The silicon device layer 16 can have a thicknessfrom 200 nm to 1000 nm. Other thicknesses that are lesser than, orgreater than, the aforementioned thickness values may also be used asthe thickness of the silicon device layer 16.

Referring now to FIG. 2, there is illustrated the exemplarysemiconductor structure of FIG. 1 after forming a deep trench 18 thatexposes a sub-surface 10A of the base silicon substrate 10. The term“sub-surface” is used throughout the present application to denote asurface of a material that is located between a topmost surface of thematerial and a bottommost surface of the material. The number of deeptrenches may vary so long as at least one deep trench is formed. By wayof one example, FIG. 2 illustrates the presence of two deep trenches 18.

The deep trench 18 can be formed utilizing a patterning process. In oneexample, the patterning process used to form the deep trench 18 mayinclude photolithography and etching. The lithographic process includesforming a photoresist (not shown) atop a material or material stack tobe patterned, i.e., the exemplary semiconductor structure shown in FIG.1, exposing the photoresist to a desired pattern of radiation, anddeveloping the exposed photoresist utilizing a conventional resistdeveloper. The photoresist may be a positive-tone photoresist, anegative-tone photoresist or a hybrid-tone photoresist. The etchingprocess includes a dry etching process (such as, for example, reactiveion etching, ion beam etching, plasma etching or laser ablation).Typically, reactive ion etching is used in providing the deep trench 18.

The deep trench 18 may have a depth from 500 nm to 10 μm. Other depthsfor the deep trench 18 are possible depending on the thickness of thesilicon device layer 16, the number of layers within the semiconductormaterial stack MS1 and the thickness of the base silicon substrate 10.The deep trench 18 that is formed has sidewall surfaces that arevertical relative to the exposed sub-surface 10A of the base siliconsubstrate 10.

Referring now to FIG. 3, there is illustrated the exemplarysemiconductor structure of FIG. 2 after forming a hanging spacer 20 onphysically exposed sidewall surfaces of the silicon device layer 16within the deep trench 18. Each hanging spacer 20 has a topmost surfacethat is coplanar with a topmost surface of the silicon device layer 16.In some embodiments and as shown in FIG. 3, each hanging spacer 20covers at least a portion of one of the physically exposed sidewallsurfaces of the silicon device layer 16. In such an embodiment, thebottommost surface of each hanging spacer 20 is located above abottommost surface of the silicon device layer 16. In other embodiments(not shown), each hanging spacer 20 entirely covers one of thephysically exposed sidewall surfaces of the silicon device layer 16. Insuch an embodiment, the bottommost surface of each hanging spacer 20 iscoplanar with the bottommost surface of the silicon device layer 16.

Each hanging spacer 20 may be formed utilizing conventional techniqueswell known to those skilled in the art. In one example, each hangingspacer 20 is formed by first forming a sacrificial dielectric material(not shown) such as, for example, an oxide or nitride, partially withinthe deep trench 18. Next, a spacer dielectric material (not shown) isformed on all exposed surfaces of the exemplary semiconductor structureutilizing a deposition process such as, for example, chemical vapordeposition (CVD) or plasma enhanced chemical vapor deposition (PECVD)and thereafter an etch is employed to remove the spacer dielectricmaterial from all horizontal surfaces of the exemplary semiconductorstructure. The dielectric spacer material that remains after the etchprovides the hanging spacer 20. After etching, the entirety of thesacrificial dielectric material is removed from the deep trench 18.

The spacer dielectric material that is used in providing the hangingspacer 20 is composed of a different dielectric material than thesacrificial dielectric material. For example, and when the sacrificialdielectric material is composed of an oxide, the spacer dielectricmaterial is composed of a nitride such as, for example, silicon nitrideor silicon oxynitride. In another example, and when the sacrificialdielectric material is composed of a nitride, the spacer dielectricmaterial is composed of an oxide such as, for example; silicon dioxide.

Each hanging spacer 20 may have a width, as measured from one sidewallto an opposing sidewall, of from 1 nm to 20 nm. Other widths arepossible and are not excluded from being used in the present applicationas the width of each hanging spacer 20 as long as the other widths donot entirely pinch off the opening of the deep trench 18.

Referring now to FIG. 4A, there is illustrated the exemplarysemiconductor structure of FIG. 3 after performing a crystallographicetch in the deep trench 18 that etches the layers of silicon selectiveto layers of boron doped silicon, wherein the etched silicon surfaces inthe deep trench 18 have a faceted sidewall surface 22. FIG. 4Billustrates an exemplary semiconductor structure such as shown in FIG.4A with less layers within the semiconductor material stack; thisdrawing was provided for clarity and will be used in the remainingdrawings of the present application.

Prior to performing the etch, an etch mask (not shown) can be formedupon the topmost surface of the silicon device layer 16 and the etchmask can be removed after the etch utilizing techniques well known tothose skilled in the art. The etch mask may be composed of a dielectricmaterial or dielectric material stack and can be removed afterperforming the crystallographic etch.

The term “faceted sidewall surface” is used in the present applicationto a denote sidewall surface that is non-vertical relative to ahorizontal plane. In one example, each faceted sidewall surface 22 maybe a (111) bound silicon surface. In such an embodiment, sigma shapedregions can be formed between opposing faceted sidewall surfaces 22within the deep trench 18. In the present application, the hangingspacer 20 serve as an etch mask during the crystallographic etch, and assuch, the crystallographic etch does not etch the silicon device layer16. The crystallographic etch does etch the various silicon layers(e.g., 14A, 14B, 14C, 14D) of the semiconductor material stack MS1, aswell as the base silicon substrate 10. With respect to the base siliconsubstrate 10, the crystallographic etch also etches silicon beneath thesub-surface 10A and can provide a pointed bottommost surface 23. In oneexample, the crystallographic etch that can be employed in the presentapplication may include a sigma etch that includes tetramethylammoniumhydroxide (TMAH) as the wet etchant.

Referring now to FIG. 5, there is illustrated the exemplarysemiconductor structure of FIG. 4B after filling the deep trench 18 withan n-doped source material 24. The term “n-doped” refers to an impuritythat contributes free electrons to an intrinsic semiconductor material.In one example, the n-doped source material 24 is arsenic doped siliconglass (ASG). In another example, the n-doped source material 24 isphosphorus doped silicon glass (PSG).

The n-doped source material 24 can be formed utilizing a depositionprocess such as, for example, spin-on coating. In some embodiments, anetch back process or a planarization process such as, for example,chemical mechanical polishing, may follow the deposition of the n-dopedsource material 24.

As is shown, the n-doped source material 24 fills in the entirety ofeach deep trench 18 and contacts the etched sidewall surfaces of each ofthe silicon layers (e.g., 10, 14A, 14B) and the non-etched sidewallsurfaces of each boron doped silicon layer (e.g., 12A, 1B, 12C). Then-doped source material 24 has a topmost surface that is coplanar with atopmost surface of each hanging spacer 20 as well as a topmost surfaceof the silicon device layer 16.

Referring now to FIG. 6, there is illustrated the exemplarysemiconductor structure of FIG. 5 after performing an anneal. The annealdrives the n-type dopant from the n-doped source material 24 into thebase silicon substrate 10, the semiconductor material stack MS1, and atleast a lower portion of the silicon device layer 16. During thisanneal, some boron can diffuse from the boron doped silicon layers(i.e., 12A, 12B, 12C) into the silicon layers (10, 14A, 14B and 16).

The anneal forms a bulk silicon substrate that contains a lower region26 and an upper region 28. The upper region 28 is a silicon region thatincludes undoped silicon which is derived from an upper portion of thesilicon device layer 16. The lower region 26 is composed of n-dopedsilicon. Within the lower region 26 of the bulk silicon substrate, thereis alternating regions of n-doped silicon that have a first boronconcentration (i.e., boron deficient regions), and regions of n-dopedsilicon that have a second boron concentration that is greater than thefirst boron concentration (i.e., boron rich regions). The n-dopedsilicon regions that are boron deficient are labeled as element 29 inFIG. 6, while the regions of n-doped silicon that contain the secondboron concentration are labeled as element 30.

Each n-doped silicon regions that is boron deficient (i.e., region 29 inFIG. 6) has an n-type dopant concentration from 1E19 atoms/cm³ to 5E20atoms/cm³ and a trace amount of boron (i.e., 1E16 atoms/cm³ to 1E17atoms/cm³), especially near the former location of the boron dopedsilicon layers. Each n-doped silicon region that contains the secondboron concentration (i.e., region 30 in FIG. 6) has an n-type dopantconcentration from 1E19 atoms/cm³ to 5E20 atoms/cm³ and a boron dopantconcentration of 1E17 atoms/cm³ to 1E18 atoms/cm³.

The anneal that can be performed in the present application may beperformed at any temperature that is capable of causing diffusion ofn-type dopant from the n-doped source material 24 into the precursorbulk semiconductor substrate (10, MS1, 16). In one embodiment, theanneal may be performed at a temperature from 900° C. to 1200° C. Theanneal is typically performed in an inert ambient such as, for example,one of argon, neon or xenon, or a forming gas ambient. The anneal may beperformed utilizing a furnace anneal, or a laser anneal and the durationof the anneal may vary depending on the type of anneal process that isperformed.

Referring now to FIG. 7, there is illustrated the exemplarysemiconductor structure of FIG. 6 after removing the n-doped sourcematerial 24 and each hanging spacer 20 from the deep trench 18. Then-doped source material 24 and each hanging spacer 20 can be removedutilizing one or more material removal processes. In one example, then-doped source material 24 may be removed utilizing a first etchingprocess, and thereafter each hanging spacer 20 can be removed utilizinga second etching process that differs from the first etching process.The removal of the n-doped source material 24 and each hanging spacer 20from the deep trench 18 exposes silicon surfaces within the deep trench18 that is present in the bulk silicon substrate (26, 28, 29, 30).

Referring now to FIG. 8, there is illustrated the exemplarysemiconductor structure of FIG. 7 after forming a first conductive layer32. The first conductive layer 32 is a continuous layer that is formedon the topmost surface of the bulk silicon substrate (26, 28, 29, 30)and along the exposed surfaces of the bulk silicon substrate (26, 28,29, 30) exposed by the deep trench 18. The first conductive layer 32will subsequently provide the bottom conductive electrode of a deeptrench capacitor.

The first conductive layer 32 that is employed in the presentapplication is composed of a metal-containing conductive material suchas, for example, a conductive metal (such as, for example, tungsten), aconductive metal nitride (such as, for example, tungsten nitride, ortitanium nitride) or a multilayered combination thereof. The firstconductive layer 32 may be formed utilizing a conformal depositionprocess including, but not limited to, atomic layer deposition (ALD),chemical vapor deposition (CVD) or plasma enhanced chemical vapordeposition (PECVD). The first conductive layer 32 follows the contour ofthe deep trench 18 and does not entirely fill in the deep trench 18. Inone embodiment, the first conductive layer 32 has a thickness from 2 nmto 10 nm.

Referring now to FIG. 9, there is illustrated the exemplarysemiconductor structure of FIG. 8 after forming a dielectric materiallayer 34. The dielectric material layer 34 is continuous layer that isformed on the entirety of the first conductive layer 32. The dielectricmaterial layer 34 will subsequently provide the node dielectric of thedeep trench capacitor.

The dielectric material layer 34 may comprise any dielectric materialappropriate for forming a trench capacitor, including but not limitedto, silicon dioxide, silicon nitride, silicon oxynitride, a high-kmaterial having a relative permittivity above about 8, or anycombination of these dielectric materials. Examples of high-k materialsinclude, but are not limited to, hafnium oxide, hafnium silicon oxide,hafnium silicon oxynitride, aluminum oxide, zirconium oxide, and anycombination of these materials.

The dielectric material layer 34 may be formed by utilizing a depositionprocess such as, for example, atomic layer deposition (ALD), molecularlayer deposition (MLD), chemical vapor deposition (CVD), or plasmaenhanced chemical vapor deposition (PECVD. The dielectric material layer34 follows the contour of the deep trench 18 and does not entirely fillin the deep trench 18. In one embodiment, the dielectric material layer34 has a thickness from 1 nm to 5 nm.

Referring now to FIG. 10, there is illustrated the exemplarysemiconductor structure of FIG. 9 after forming a second conductivelayer 36. The second conductive layer 36 is continuous layer that isformed on the entirety of the dielectric material 34 and entirely fillsthe remaining volume of the deep trench 18. The second conductive layer36 will subsequently provide the top conductive electrode of the deeptrench capacitor.

In one embodiment, the second conductive layer 36 that is employed inthe present application is composed of a metal-containing conductivematerial such as, for example, a conductive metal (such as, for example,tungsten), a conductive metal nitride (such as, for example, tungstennitride, or titanium nitride) or a multilayered combination thereof. Insuch an embodiment, the metal-containing conductive material thatprovides the second conductive layer 36 may, or may not, be the same asthe metal-containing conductive material that provides the firstconductive layer 32. In another embodiment, the second conductive layer36 may be composed of a doped polycrystalline semiconductor materialsuch as, for example, arsenic doped polysilicon.

The second conductive layer 36 may be formed utilizing a conformaldeposition process including, but not limited to, atomic layerdeposition (ALD), chemical vapor deposition (CVD) or plasma enhancedchemical vapor deposition (PECVD). The second conductive layer 36 mayinclude an overburden upper portion that is formed outside the deeptrench 18.

Referring now to FIG. 11, there is illustrated the exemplarysemiconductor structure of FIG. 10 after removing portions of the firstconductive layer 32, the dielectric material layer 34 and the secondconductive layer 36 that are present outside the deep trench 18, whilemaintaining portions of the first conductive layer 32, the dielectricmaterial layer 34 and the second conductive layer 36 that are presentinside the deep trench 18. The remaining first conductive layer 32within the deep trench 18 may be referred to herein as a bottomelectrode plate 32P, the remaining dielectric material layer 34 withinthe deep trench may be referred to as a node dielectric 34L, and theremaining second conductive layer 36 in the deep trench may be referredto herein as a top conductive plate 36P. Collectively, the bottomelectrode plate 32P, the node dielectric 34L, and the top electrodeplate 36P constitute the deep trench capacitor of the presentapplication.

The removal of portions of the first conductive layer 32, the dielectricmaterial layer 34 and the second conductive layer 36 that are presentoutside the deep trench 18 may be performed utilizing one or morematerial removal processes. In one embodiment, the one or more materialremoval processes include a planarization process such as, chemicalmechanical polishing and/or grinding.

At this point of the present application, the bottom electrode plate32P, the node dielectric 34L, and the top electrode plate 36P havetopmost surfaces that are coplanar with each other as well as beingcoplanar with a topmost surface of the upper portion 28 of the bulksilicon substrate.

Semiconductor devices including, for example, transistors may now beformed upon, and within the upper portion 28 of the bulk siliconsubstrate utilizing conventional techniques well known in the art.

Referring now to FIG. 12, there is illustrated the exemplarysemiconductor structure of FIG. 11 after forming a deep trench contact38. A single deep trench contact is formed for each deep trenchcapacitor that is formed. Each deep trench contact 38 extends from thetopmost surface of the upper portion 28 of the bulk silicon substrateand into a bottommost n-doped silicon region that is boron deficient andthat is present in the lower region 26 of the bulk silicon substrate.

Each deep trench contact 38 may include a contact metal or metal alloysuch as, for example, copper, aluminum, cobalt, or a copper-aluminumalloy. Each deep trench contact 38 may be formed by first providing adeep contact trench (not shown) into the bulk silicon substrate (26, 28,29, 30), and then filling the deep contact trench with a contact metalor metal alloy. The filling of the deep contact trench may include adeposition process and a planarization process may follow the deepcontact trench fill.

Each deep trench contact 38 has a topmost surface that is coplanar withthe topmost surface of each element of the deep trench capacitor (32P,34L, 36P) as well as the topmost surface of the upper region 28 of thebulk silicon substrate.

FIGS. 11 and 12 illustrate a semiconductor structure in accordance withan embodiment of the present application. In the illustrated embodiment,the semiconductor structure includes a deep trench capacitor (32P, 34L,36P) present in a deep trench 18 having faceted sidewall surfaces 22that is located in a bulk silicon substrate (26, 28, 29, 30), whereinthe bulk silicon substrate includes an upper region 28 of undopedsilicon and a lower region 26 of n-doped silicon, wherein the lowerregion 28 comprises alternating regions of n-doped silicon that have thefirst boron concentration (i.e., boron deficient regions 29), andregions of n-doped silicon that have the second boron concentration(i.e., boron rich regions 30).

Referring now to FIG. 13, there is illustrated another exemplarysemiconductor structure of the present application. The exemplarysemiconductor structure of FIG. 13 is similar to the one shown in FIG.12 except that a flowable dielectric material 40 such as, a flowableoxide, is formed within a lower portion of one of the deep trenches 18.As is shown, the flowable dielectric material 40 is located in a lowerportion of one of the deep trenches 18 and is located entirely beneathone of the deep trench capacitors (32P, 34L, 36P). The flowabledielectric material 40 may be formed into any number of regions withinthe deep trench 18 prior to forming the deep trench capacitor (32P, 34L,36P). This allows for tailoring the capacitance value of any given deeptrench capacitor (32P, 34L, 36P). In the illustrated example, the deeptrench capacitor (32P, 34L, 36P) on the far left hand side of thedrawing has a different capacitance than the deep trench capacitor (32P,34L, 36P) on the far right hand side of the drawing.

In FIG. 13, a semiconductor structure is provided that includes a firstdeep trench capacitor (32P, 34L, 36P on the far left hand side) presentin a first deep trench 18 having faceted sidewall surfaces 22 that islocated in a bulk silicon substrate (26, 28, 29, 30), wherein the bulksilicon substrate includes an upper region 28 of undoped silicon and alower region 26 of n-doped silicon, wherein the lower region 26comprises alternating regions of n-doped silicon that have the firstboron concentration (i.e., boron deficient regions 29), and regions ofn-doped silicon that have the second boron concentration (i.e., boronrich regions 30). A second deep trench capacitor (32P, 34L, 36P on thefar right hand side) is present in a second deep trench 18 havingfaceted sidewall surfaces 22 that is located in the bulk siliconsubstrate (26, 28, 29, 30), wherein a flowable dielectric material 40 islocated in a lower portion of the second deep trench 18 and locatedentirely beneath the second deep trench capacitor (32P, 34L, 36P on thefar right hand side).

Tailoring of the capacitance of each deep trench capacitor (32P, 34L,36P) can be provided by the shape of the deep trench 18 that is formedafter performing the crystallographic etch, and/or by forming a flowabledielectric material 40 within some portions of the deep trench 18 afterperforming the crystallographic etch.

While the present application has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present application. It is therefore intended that the presentapplication not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A semiconductor structure comprising: a deeptrench capacitor present in a deep trench having faceted sidewallsurfaces that is located in a bulk silicon substrate, wherein the bulksilicon substrate includes an upper region of undoped silicon and alower region of n-doped silicon, wherein the lower region comprisesalternating regions of n-doped silicon that have a first boronconcentration, and regions of n-doped silicon that have a second boronconcentration which is greater than the first boron concentration. 2.The semiconductor structure of claim 1, further comprising a flowabledielectric material located in a lower portion of the deep trench andlocated entirely beneath the deep trench capacitor.
 3. The semiconductorstructure of claim 1, wherein an area in the deep trench that is locatedbetween opposing faceted sidewall surfaces has a sigma shape.
 4. Thesemiconductor structure of claim 3, wherein the faceted sidewallsurfaces are (111) bound silicon surfaces.
 5. The semiconductorstructure of claim 1, wherein the lower region of n-doped siliconcomprises arsenic or phosphorus as the n-type dopant.
 6. Thesemiconductor structure of claim 1, wherein the second boronconcentration is from 1E17 atoms/cm³ to 1E18 atoms/cm³.
 7. Thesemiconductor structure of claim 1, wherein the deep trench capacitorcomprises a bottom electrode plate, a node dielectric, and a topelectrode plate, wherein each of the bottom electrode plate, the nodedielectric, and the top electrode plate has a topmost surface that iscoplanar with each other as well as being coplanar with a topmostsurface of the upper portion of the bulk silicon substrate.
 8. Thesemiconductor structure of claim 7, wherein the deep trench capacitorextends into a bottommost region of n-doped silicon that has the firstboron concentration.
 9. The semiconductor structure of claim 1, furthercomprising a deep trench contact, wherein the deep trench contactextends into the bottommost region of n-doped silicon that has the firstboron concentration.
 10. A semiconductor structure comprising: a firstdeep trench capacitor present in a first deep trench having facetedsidewall surfaces that is located in a bulk silicon substrate, whereinthe bulk silicon substrate includes an upper region of undoped siliconand a lower region of n-doped silicon, wherein the lower regioncomprises alternating regions of n-doped silicon that have a first boronconcentration, and regions of n-doped silicon that have a second boronconcentration which is greater than the first boron concentration; and asecond deep trench capacitor present in a second deep trench havingfaceted sidewall surfaces that is located in the bulk silicon substrate,wherein a flowable dielectric material is located in a lower portion ofthe second deep trench and located entirely beneath the second deeptrench capacitor.